The gas that the born-again AGB star ejects might be H-poor and He-poor (e.g., [1]}). The inflated envelope of the born-again star in these cases is H-poor and He-poor. However, calculations show that the inflated envelope can be H-rich and He-rich as well (e.g., [2]}).
The envelope can be also He-rich and H-poor, as with V605 Aql, the central star of the planetary nebula A58 (e.g., [3]}).
